I'm near Edmonton. Zone 3. Suppose I took a zone 5 hardy Japanese maple, like Emporer's Blood and put it in a #15 pot with insulated sides. In the fall, leave it out until leave fall. Put it on a concrete pad, and pile around with strawbales or dried leaves. This allows the ground temps to stabilize the root ball temps. When temps get down to zone 5'ish (-25 C) bring it into a cool room with south facing window. Keep inside until frost danger is past. Move out to the deck. So the plant would have 3 locations during the year. *** How does A. palmetum determine when to break bud? Temperature, day length? Does it have a chilling requirement? This is essentially creating an 8 month growing season for it. Would the leaves wear out in that time?
I think palmatum has a chilling time requirement and after it is met, bud break is determined by temperature. So, one's weather could be cold (below 40F/5C) for a while and then have a subsequent period of time with temperatures always above 40F/5C and buds do not move. A subsequent cold period could last long enough to accumulate the bud chilling hours and the buds will break when temperatures rise again. I do not know what the chilling hours are, but I think it is maybe as long as 1000 hours (6 weeks). Further, I am certain it changes with the cultivar. I have 'Orange Dream' that is always the first palmatum to leaf out, a generic green is next, then my 'Shindeshojo' and 'Higasayama', etc., and 'Akashigatatsusawa' is always the last. I do believe this is because of lengthier bud chilling times for each cultivar as I've ordered them. Day length is sensed by leaves and since there are none, I don't believe bud break is initiated by day length. Stems are green and cambium does have chromophores that conceivably could. Were this the case, bud break times would vary with age of the tree. I haven't noticed any such trend in my trees over the last decade or so. The effect may exist but is so subtle that a careful scientific investigation would be needed to convince me otherwise. Lastly, concerning growing season, palmatums will flush at least twice in a season though it is common that there are three periods of extensive growth, one ending about May, one ending about August, and the last at leaf fall. IOW you will not have an entire tree with nothing but leaves from the first flush. Furthermore, one can partially defoliate any palmatum to keep leaves from being 'shaded out' and to simply remove ugly leaves as is commonly done in bonsai practice.
